Mean Age of Air

payam1362 · May 7, 2018, 03:33

Dear All member
I have problem to define mean age of air as a new scalar in fluent particularly about the boundary condition definition.

So any help is highly appreciated.

pakk · May 7, 2018, 04:24

If you want help with your problem, you have to explain what your problem is.

payam1362 · May 7, 2018, 04:37

In simple word, my model has a room with two windows (one as the opening and other as the exit of the air). when I want to define the boundary conditions, I should define the scalar of (mean age of air) as 0 in the opening. But the problem is in the inlet and outlet of the domain, also the scalar is defined as 0 which is not correct (only for the opening should be zero).

Thank you very much

pakk · May 7, 2018, 04:43

I am already confused why you think this should be a scalar (by which I assume you mean UDS, User-Defined Scalar).

payam1362 · May 7, 2018, 05:01

yes, you are right it is user defined scalar.

pakk · May 7, 2018, 07:27

And I don't understand how "mean age of air" can have the properties that a UDS has. What would diffusion of a mean age even mean? It makes no sense.

You are using the wrong tool for this job.

You probably want to know how long a 'molecule' has been in your simulation domain. Which is an interesting question, not easy to answer but certainly doable. But a UDS is not the right tool for that.

My idea would be to use a UDM to store the information, and use a UDF to fill the UDM. Alternatively, it might be possible to use a custom field function to calculate this.

The difficult part is to write a UDF to fill the UDM. It is certainly possible, but it would take me too much time to do for free on this forum.

May 7, 2018, 03:33	Mean Age of Air	#1
payam1362 New Member payam Join Date: Dec 2012 Posts: 4 Rep Power: 14	Dear All member I have problem to define mean age of air as a new scalar in fluent particularly about the boundary condition definition. So any help is highly appreciated.

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May 7, 2018, 04:24		#2
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	If you want help with your problem, you have to explain what your problem is.

May 7, 2018, 04:37		#3
payam1362 New Member payam Join Date: Dec 2012 Posts: 4 Rep Power: 14	In simple word, my model has a room with two windows (one as the opening and other as the exit of the air). when I want to define the boundary conditions, I should define the scalar of (mean age of air) as 0 in the opening. But the problem is in the inlet and outlet of the domain, also the scalar is defined as 0 which is not correct (only for the opening should be zero). Thank you very much

May 7, 2018, 04:43		#4
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	I am already confused why you think this should be a scalar (by which I assume you mean UDS, User-Defined Scalar).

May 7, 2018, 05:01		#5
payam1362 New Member payam Join Date: Dec 2012 Posts: 4 Rep Power: 14	yes, you are right it is user defined scalar.

May 7, 2018, 07:27		#6
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	And I don't understand how "mean age of air" can have the properties that a UDS has. What would diffusion of a mean age even mean? It makes no sense. You are using the wrong tool for this job. You probably want to know how long a 'molecule' has been in your simulation domain. Which is an interesting question, not easy to answer but certainly doable. But a UDS is not the right tool for that. My idea would be to use a UDM to store the information, and use a UDF to fill the UDM. Alternatively, it might be possible to use a custom field function to calculate this. The difficult part is to write a UDF to fill the UDM. It is certainly possible, but it would take me too much time to do for free on this forum.